Question

Sol.(b) [Key Concept: Haemophilia — X-linked Recessive Disorder] Haemophilia is MOST APPROPRIATELY described as an X-LINKED RECESSIVE GENE DISORDER. Haemophilia A (Factor VIII deficiency) and Haemophilia B (Factor IX deficiency, Christmas disease) are both caused by recessive mutations in genes on the X chromosome. Males (XY) with one mutant X allele are affected; females (XX) require two mutant X alleles to be affected (very rare). Carriers (X^H X^h females) are phenotypically normal. It is a genetic (single gene) disorder, not a chromosomal disorder.